1. Field of the Invention
This invention relates to a component built-in board having an electronic component built in thereto, and a method of manufacturing the same.
2. Description of the Prior Art
A known countermeasure for heat radiation from a board having an electronic component mounted thereon or built in thereto is, for example, a structure such as that of the ceramic wiring board disclosed in Japanese Unexamined Patent Application Publication No. 2006-41242 A described below. This ceramic wiring board includes a heat radiation-dedicated via (thermal via) formed penetrating in a substantially vertical direction from a front surface to a rear surface of an insulating base. Moreover, in the ceramic wiring board, a diameter of a heat radiation-dedicated via on a front surface side at a place where the electronic component is mounted is formed smaller than a diameter of another heat radiation-dedicated via. This is said to result in unevenness of the board being absorbed by a difference in level of heat radiation-dedicated vias of different diameters while heat radiation properties are maintained, whereby flatness of a board front surface overall can be secured.
However, in the heat radiation countermeasure of conventional technology disclosed in above-described Japanese Unexamined Patent Application Publication No. 2006-41242 A, the diameter of the heat radiation-dedicated via directly connected to the electronic component is small, hence it is difficult to say that the countermeasure is a structure where heat from the electronic component is necessarily transferred efficiently. Moreover, there is a problem that when the number of heat radiation-dedicated vias of small diameter is increased in order to improve heat radiation characteristics, processing steps become complicated and there is a limit to processing accuracy, hence not such a large improvement in heat radiation characteristics can be expected. Furthermore, the above-described structure is assumed to be even less effective particularly in a component built-in board having an electronic component built in thereto.